1. Field of the Invention
The present invention relates generally to an antenna, and more particularly to a multi-band antenna for use with an electronic device.
2. Description of the Prior Art
The prosperous development of wireless communication industry brings various products and techniques for multi-band communication such that many new products have the performance for wireless communication so as to meet the consumers' demand. Such products as WLAN cards with antennas on/in them for use with a laptop computer or a personal digital assistance (PDA) are gaining popularity in wireless communication market. These cards benefit from multi-band antennas operated under IEEE 802.11a/b/g standard. In most cases, embedded multi-band antennas are arranged in an electronic device directly, rather than via a WLAN card. Whatever, a multi-band antenna with small size and high performance is essential and critical to achieve the purpose for wireless communication.
A series of dual-band antennas embedded within electronic devices are disclosed in U.S. patent application Publication No. 2003/0222823, including slot-slot antenna, PIFA-PIFA antenna, and PIFA-slot antenna, and so on. Take a general architecture of a PIFA-PIFA antenna for example. The dual-band antenna 700 comprises a first radiating element comprising components 702 and 703, and a second radiating element comprising components 704 and 708. The first and the second radiating elements are connected to a ground element 701. An antenna feed is preferably implemented using a coaxial transmission line 706, wherein an inner conductor 705 of the coaxial transmission line is connected to the first radiating element, and an outer conductor 707 of the coaxial transmission line is connected to the ground element 701. The antenna 700 operates in a lower frequency band of about 2.4 GHz to about 2.5 GHz under IEEE 802.11b/g and a higher frequency band of about 5.15 GHz to about 5.35 GHz under IEEE 802.11a. However, the antenna cannot be used in another frequency band of 5.75–5.825 GHz which is also under IEEE 802.11a standard. Moreover, the lower and the higher frequency bands of the antenna are narrow, which restrains the application of the antenna. Additionally, the second radiating element of the antenna is fed though coupling, rather than by the coaxial transmission line directly, which reversely affects the antenna gain.
Hence, in this art, a multi-band antenna with wide bandwidth to overcome the above-mentioned disadvantages of the prior art will be described in detail in the following embodiments.